One in five men over 60 have below-normal testosterone levels. That number jumps to half of all men over 8020. The soy vs dairy testosterone debate has concerned aging men for years. Many wonder which protein source is safer for their hormone health. Soy contains plant estrogens that raise concerns about whether it affects testosterone. Dairy products provide 60-80% of the female sex steroids consumed in human diets20. Research perusing does soy decrease in testosterone versus does milk lower testosterone reveals unexpected findings about soy-based foods that lower testosterone in older men.
Understanding Testosterone in Men Over 60
Why testosterone matters for aging men
The testicles produce testosterone and this hormone drives multiple biological processes beyond sexual function. The hormone maintains bone density, regulates fat distribution, supports muscle strength and mass, controls red blood cell production, and influences facial and body hair growth1. These functions become vulnerable as men age, making testosterone especially important for men over 60.
The hormone operates through two main mechanisms. Free testosterone binds to androgen receptors, while some testosterone converts to estradiol through aromatization. This affects bone, adipose tissue, and brain function21. Testosterone also transforms into dihydrotestosterone (DHT), which binds to the same receptors with five times more potency than testosterone itself21.
Beyond physical attributes, testosterone influences mood and cognition, metabolism, immune function, and cardiovascular health3. Low levels increase the risk of diabetes, dementia, cardiovascular disease, and mortality in aging males3. The hormone also gets proteins that encourage muscle growth, making adequate levels essential to maintain muscle strength, power, and endurance21.
Natural decline and health effects
Testosterone production peaks during adolescence and early adulthood, with maximum levels reached around age 172. Healthy young men produce about six milligrams of testosterone daily2. The decline begins around age 30 to 40, dropping at a rate of 1% annually14. Some research indicates total serum testosterone decreases at 0.4% per year in men aged 40-70, while free testosterone shows a more pronounced decline of 1.3% each year3.
By age 70, average testosterone production sits 30% below peak levels2. Despite this decline, testosterone levels remain within the normal range in at least 75% of older men2. Only 10% to 25% of older men have levels considered low4.
The aging process affects testosterone through multiple pathways. Reduced GnRH secretion from the hypothalamus represents the main cause of decreased LH secretion in older individuals, accompanied by attenuated Leydig cell responsiveness to LH stimulation3. Chronic inflammation emerges as a hallmark of aging, with inflammatory cytokines like TNF-α, IL-1β, IL-6, and IL-8 upregulated by a lot in aged testicular tissue and this disrupts the testicular microenvironment3.
Physical changes from low testosterone include increased body fat, reduced muscle bulk and strength, decreased bone density, and potential gynecomastia1. Men experience reduced sexual desire, fewer spontaneous erections, and possible infertility1. Emotional changes show as decreased motivation, sadness, depression, or difficulty concentrating1. After age 60, muscle mass decline accelerates because men produce less testosterone while becoming less active5.
Normal testosterone ranges span 270 to 1,070 ng/dL, with production highest at 8 a.m. and lowest at 9 p.m.2. Men over 50 with total testosterone below 200 ng/dL are considered hypogonadal, while levels between 200 and 400 ng/dL fall into a borderline category that requires additional testing2.
How diet may influence hormone levels
Large energy deficits affect testosterone concentrations negatively. Studies show a 40% reduction in total caloric intake decreases circulating testosterone, even when protein sources comprise a high percentage of calories21. Low energy availability, defined as less than 30 kcal per kg of fat-free mass daily, decreases LH concentrations and reduce testosterone levels in the body synthesis21.
Dietary fat type affects hormone levels. Trans fats may affect testosterone negatively, as opposed to polyunsaturated omega-3 fatty acids, which may increase testicle size and improve function6. Men who consume fewer dark green vegetables show higher likelihood of low serum testosterone and hypogonadism7. Zinc and vitamin D deficiencies can affect testosterone levels, as these nutrients play roles in maintaining optimal hormone concentrations7.
Western-style diets high in refined carbohydrates and added sugars associate with lower testosterone levels8. Obesity, insulin resistance, stress, and poor sleep patterns worsen symptoms of testosterone decline8. This creates a cycle where decreased energy discourages exercise and leads to further muscle loss and weight gain, which decrease in testosterone levels 9.
Soy vs Dairy Testosterone: What Research Shows
What are phytoestrogens and isoflavones
Isoflavones represent a class of plant estrogens, which are plant-derived compounds with estrogenic activity22. These polyphenolic molecules are similar to endogenous human hormones, hence their estrogenic properties23. Soy stands as the main dietary source of these plant secondary metabolites, though fruits and vegetables contain them in lesser amounts23.
The highest soy-derived isoflavone intakes worldwide occur in China and Japan, where populations consume an average of 15-50 mg per day, compared to only about 2 mg per day in Western countries23. Mediterranean countries show the lowest average intake. Northern countries reach 0.76 mg/day23.
Do soy phytoestrogens mimic estrogen
Soy isoflavones bind to estrogen receptors within cells due to their similarity with 17-β-estradiol22. But they preferentially bind to and activate estrogen receptor-β (ER-β) rather than ER-α, whereas estrogen has equal affinity for both receptors10. This binding preference matters because the two receptors have different tissue distributions and can exert different, sometimes opposite physiological effects10.
Levels of isoflavones in response to ingesting about two servings of traditional soyfoods are three orders of magnitude higher than estrogen10. Despite these elevated levels, the preference for ER-β allows isoflavones to have tissue-selective effects, leading scientists to classify them as selective estrogen receptor modulators (SERMs)10.
Clinical studies on soy effects on men
Animal studies raised concerns about soy's hormonal effects at first. A study in rats fed a phytoestrogen-rich diet containing about 600 microg/g isoflavones showed plasma testosterone and androstenedione levels were substantially lower compared with animals fed a phytoestrogen-free diet24. But these animal findings face substantial limitations when applied to human health assessments. Rodents have less efficient phase II metabolism via glucuronidation, leading to much higher plasma concentrations of unconjugated genistein than humans12.
Does soy lower testosterone levels
A complete meta-analysis of 41 studies measuring testosterone levels in 1,753 men found no significant effects of soy protein or isoflavone intake on total testosterone, free testosterone, estradiol, or estrone levels25. These results held whatever the isoflavone dose and study duration25. Sub-analysis according to dose (≤75 mg/d vs >75 mg/d) and duration (≤12 weeks vs >12 weeks) also showed no effect10.
An earlier meta-analysis reached similar conclusions and found that neither soy foods nor isoflavone supplements alter measures of bioavailable testosterone concentrations in men26. One Japanese study in healthy male volunteers consuming 60 mg per day of soy isoflavones showed serum levels of SHBG increased while free testosterone decreased23. But total testosterone remained unchanged23.
Dairy Milk's Hormonal Impact on Older Men
Natural hormones present in dairy milk
Modern dairy farming is very different from historical practices. Cows now produce milk throughout most of their pregnancy. This creates big changes in hormone composition11. Artificial insemination practices keep dairy cows pregnant during lactation periods and allow nearly continuous milk harvesting11.
Pregnant cows lactate, so their milk contains higher levels of mammalian sex hormones. Cow's milk contains steroid hormones like progesterone, 17β-estradiol, estrone and estradiol. It also has protein hormones like IGF-12728. More than 50 different hormones exist in dairy milk29.
Hormone concentrations change a lot based on pregnancy status. Estrone rises from 7.9 ng/L in non-pregnant cows to 1,266 ng/L during the third trimester11. The same pattern appears with 17β-estradiol, which increases from 18.6 to 51.2 ng/L during pregnancy11. The levels of 17α-E2 climb from 33 to 322 ng/L11. Cows spend extended periods pregnant while lactating, so these pregnancy-related hormones accumulate in commercially available milk11.
Effect of dairy on testosterone in elderly men
Studies show mixed results on how dairy affects testosterone. One study showed that men who consumed milk experienced rising serum estrone and progesterone levels within an hour30. Their testosterone, luteinizing hormone and follicle-stimulating endocrine system dropped within 60 minutes of drinking milk30. The milk's estrogens entered the bloodstream and reduced gonadotropin secretion. This led to decreased testosterone production30.
But another study found no changes in circulating testosterone after dairy consumption11. This study thought that dairy milk would lower testosterone compared to soy due to high progesterone content. Yet it observed equivalent acute serum sex hormone concentrations after soy consumption 11.
These different results show that individual factors influence hormonal responses. Metabolic differences, overall dietary patterns, age and baseline hormone levels all play a role. Consumption frequency matters too.
Organic vs conventional dairy differences
Organic dairy prohibits recombinant bovine somatotropin, a synthetic growth hormone used to boost milk production31. Residues of bovine growth hormone were 20 times higher in conventional milk than organic15. Conventional milk samples tested positive for antibiotic residues and pesticides. Organic milk showed no such contaminants15.
Both types contain natural hormones though. Scientific findings show no big differences in estrogen levels between conventional and organic products28. Processing through pasteurization and homogenization has little effect on estrogen concentrations28.
Direct Comparison: Soy vs Dairy Testosterone Effects
Clinical trial results in men
A pilot study compared soy and dairy milk consumption directly. The study found no significant differences in acute circulating serum for free testosterone, percentage free testosterone, and total testosterone between the two beverages11. Progesterone and estrogen levels remained equivalent between milk conditions11. The area under the curve analysis showed no differences for any hormones measured11.
Researchers hypothesized dairy milk would raise circulating estrogen levels due to high concentrations of sex hormones in commercial dairy products. This hypothesis assumed hormones in commercial dairy milk translate into elevated concentrations of circulating sex hormones in humans11. The study results contradicted this assumption and showed both free and total testosterone concentrations were equivalent between groups11.
A complete meta-analysis of 41 studies with 1,753 men confirmed no significant effects of protein or isoflavone intake on total testosterone, sex hormone binding globulin, free testosterone, or free androgen index16. The pooled effect of isoflavone consumption on hormonal profile showed no statistical significance16.
Short-term vs long-term hormonal changes
Sub-analysis according to study duration revealed no effect on testosterone levels whatever the timeframe. Studies lasting 12 weeks or less showed similar results to those exceeding 12 weeks10. None of the four longer-term studies lasting 12 months or more found statistically significant effects on testosterone levels10.
The lack of duration-dependent effects held true for dose variations. Analysis comparing intakes of 75 mg/d or less versus more than 75 mg/d isoflavones showed no differences10. This dose threshold covers high soy intake by Asian standards and is equivalent to about three servings of traditional soyfoods10.
SHBG and free testosterone comparisons
Sex hormone-binding globulin measurements showed no statistical differences between soy and dairy milk conditions11. The 2010 meta-analysis found neither soy foods nor isoflavone supplements alter measures of bioavailable testosterone concentrations in men10.
Protein Quality and Muscle Health Considerations
Leucine content in soy vs dairy
Whey protein naturally contains 10-12% leucine, while soy products: nuts, spearmint, peppermint, licorice root, flaxseed, omega-6 fatty acids provides 7-8%13. This amino acid serves as a molecular trigger for muscle protein synthesis through the mTOR signaling pathway13. Whey delivers approximately 2.2 grams of leucine versus 1.5 grams from soy at the time you compare equal 20-gram servings14.
Matched leucine intake between soy and dairy proteins produces equivalent lean mass gains and strength improvements during resistance training14. This finding suggests previous studies that showed whey's superiority reflected its higher leucine content rather than inherent differences in protein quality14.
Muscle protein synthesis in aging men
Acute metabolic studies reveal differing responses. Older men showed that 20-40 grams of soy protein isolate failed to raise muscle protein synthesis rates from baseline fasting levels17. Meanwhile, 20 grams of whey protein stimulated greater muscle protein synthesis compared to matched doses of casein or soy17.
But long-term training outcomes tell a different story. A meta-analysis of nine studies concluded soy supplementation produces similar gains in strength and lean body mass as whey protein in response to resistance training18. Sarcopenia affects 30% if you have over 60 and more than 50% over 8019. Research shows that consuming protein blends with soy protein and caseinate activates pathways that initiate muscle protein turnover19.
Conclusion
The soy versus dairy testosterone debate appears unfounded when we get into the scientific evidence. Research shows neither soy nor dairy substantially affects testosterone levels by 32% in men over 60, despite concerns about phytoestrogens and natural hormones. Both protein sources provide valuable nutrients for muscle health. Protein quality and leucine content matter more than hormone effects.
Men should focus on adequate protein intake and optimize key nutrients like zinc and vitamin D. Follow dietary patterns that support healthy testosterone levels. Choose between soy and dairy based on your priorities, digestive tolerance and nutritional goals instead of hormonal fears.
FAQs
Q1. Is soy milk a healthy choice for men over 60? Yes, soy can be a healthy option for men over 60. It provides valuable protein and is rich in calcium, which helps prevent osteoporosis—a condition that weakens bones in seniors. Research shows that soy consumption does not negatively affect testosterone levels, making it a safe dietary choice for older men.
Q2. Does soy milk increase estrogen levels in men? No, does not significantly increase estrogen levels in men. While soy contains plant estrogens called isoflavones, comprehensive studies involving over 1,700 men found no significant effects on estrogen, testosterone, or other hormone levels, regardless of the amount consumed or duration of intake.
Q3. Can soy milk affect prostate health in men? Milk may actually benefit prostate health. Research from the Adventist Health Study found that daily soy consumption was associated with a reduced risk of prostate cancer. Unlike high-fat dairy products, which have been linked to increased mortality, milk offers a nutritious alternative without negative prostate health effects.
Q4. Which is better for muscle health in older men—soy or dairy protein? Both soy and dairy proteins support muscle health effectively in older men. While dairy contains slightly more leucine (an amino acid important for muscle building), long-term studies show that soy and dairy produce similar gains in strength and lean muscle mass when combined with resistance training.
Q5. Does dairy milk lower testosterone levels in men? Research shows mixed results, but most evidence suggests dairy milk does not significantly lower testosterone levels. While one study showed temporary hormone fluctuations within an hour of consumption, other research found no meaningful changes in testosterone levels after dairy intake, indicating individual responses may vary.
References
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[2] - https://www.health.harvard.edu/newsletter_article/testosterone_aging_and_the_mind
[3] - https://pmc.ncbi.nlm.nih.gov/articles/PMC11562514/
[4] - https://www.mayoclinic.org/healthy-lifestyle/mens-health/in-depth/male-menopause/art-20048056
[5] - https://www.hss.edu/health-library/move-better/muscle-mass-testosterone
[6] - https://www.medicalnewstoday.com/articles/325186
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[8] - https://share.upmc.com/2020/08/testosterone-levels/
[9] - https://www.columbiadoctors.org/news/how-testosterone-changes-affect-mens-health-you-age
[10] - https://www.sciencedirect.com/science/article/pii/S0890623820302926
[11] - https://pmc.ncbi.nlm.nih.gov/articles/PMC11162160/
[12] - https://pmc.ncbi.nlm.nih.gov/articles/PMC12303811/
[13] - https://link.springer.com/article/10.1186/1743-7075-9-57
[14] - https://selp.life/blog/soy-whey-protein-leucine-matched-muscle-gains
[15] - https://www2.organic-center.org/what-does-research-say
[16] - https://www.sciencedirect.com/science/article/pii/S0015028209009662
[17] - https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/characterising-the-muscle-anabolic-potential-of-dairy-meat-and-plantbased-protein-sources-in-older-adults/B252F737A07FB6EAD62297D4432A5030
[18] - https://sniglobal.org/supplementing-plant-based-diets-with-soy-protein-increases-muscle-mass-and-strength/
[19] - https://www.nutritioninsight.com/news/soy-and-dairy-proteins-can-protect-against-sarcopenia.html
[20] - https://goldmanlaboratories.com/blogs/blog/soy-vs-dairy-testosterone-men-60?srsltid=AfmBOoqhMMjevNI6DFz2MSADfmKP3MDzk5eWaYMQqod4lQWcaK6mnOGP
[21] - https://pmc.ncbi.nlm.nih.gov/articles/PMC8538516/
[22] - https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/soy-isoflavones
[23] - https://pmc.ncbi.nlm.nih.gov/articles/PMC7468963/
[24] - https://pubmed.ncbi.nlm.nih.gov/11524239/
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